An intermittent radar echo first noticed at 2 : 05 am was ignored when nothing was seen through binoculars, and at 2 : 14 " Rena " struck the reef.
22.
A further uncertainty arises from Arecibo Radio Telescope, which could only pick up an unexpectedly weak radar echo, implying that is either smaller than estimated or reflects radio waves only weakly.
23.
The continuous time interval that the radar echo can be received is upper bounded by the time interval between the end of a transmitted pulse and the beginning of next one, say PRI-\ tau.
24.
If the two samples are obtained simultaneously ( perhaps by placing two antennas on the same aircraft, some distance apart ), then any phase difference will contain information about the angle from which the radar echo returned.
25.
By performing the radar mapping at two separated times ( before and after an event ) over the same area, the terrain shift will be shown as different phase due to path difference in the radar echo returned.
26.
A simple calculation reveals that a radar echo will take approximately 10.8 ?s to return from a target 1 statute mile away ( counting from the leading edge of the transmitter pulse ( T 0 ), ( sometimes known as transmitter main bang ) ).
27.
"" The RAX radar echo discovery has convincingly proved that miniature satellites, beyond their role as teaching tools, can provide high caliber measurements for fundamental space weather research, " " said Therese Moretto Jorgensen, Ph . D ., Geospace program director in the Division of Atmospheric and Geospace Sciences at the National Science Foundation.
28.
UN forces named the Po-2's nighttime appearance " Bedcheck Charlie " and had great difficulty in shooting it down & mdash; even though night fighters had radar as standard equipment in the 1950s, the wood-and-fabric-construction of the Po-2 gave only a minimal radar echo, making it hard for an opposing fighter pilot to acquire his target.
29.
It is not known exactly how these work or even if the capability is fully operational, but it may employ active cancellation technology, such as has been tested by Thales and MBDA . Active cancellation is supposed to work by sampling and analysing incoming radar and feeding it back to the hostile emitter out of phase thus cancelling out the returning radar echo.
